The use of unmanned aerial vehicles (UAVs) has become important in recent years for a wide variety of applications, including military uses. In some applications, a UAV may be required to have a capability for maneuvering quickly or in tight spaces. Further, the UAV may be required to have this capability over a wide range of speeds.
Conventional fixed wing small UAVs generally lack the maneuvering capability and speed range that would be necessary for operating in an urban canyon. Generally, this is due to reliance upon airflow over control surfaces derived from the forward airspeed of the vehicle. Vertical takeoff-and-landing (VTOL) aircraft have been used to address this maneuvering challenge at low speeds. For example, in U.S. Pat. No. 6,719,244, a VTOL aircraft uses lateral tilting of the propellers to induce unbalanced torque-induced and gyroscopic moments which act on the aircraft about an axis essentially perpendicular to the tilt axis. U.S. Patent Application Publication No. US 2006/0192047 discloses a hovering air vehicle that uses two ducted fans attached to a common drive housing. The vanes below each fan body can be tilted differentially or in unison to generate control forces. In one embodiment, fixed wings are attached to the ducts for forward flight capability.
However, in both of these instances, control forces are generated through secondary effects, either gyroscopic or aerodynamic. These control forces increase system complexity and limit achievable maneuverability. Therefore, the present inventors have recognized the need to develop an aircraft that has such a capability.